The present invention relates to a fuel supply system of an internal combustion engine that includes a delivery pipe provided with a relief valve, which discharges fuel when being opened, and to the internal combustion engine.
Japanese Laid-Open Patent Publication No. 7-103048 discloses an internal combustion engine that distributes fuel accumulated in a delivery pipe to injectors of cylinders. In an internal combustion engine in which the fuel pressure in a delivery pipe is high, for example, in an in-cylinder injection gasoline engine or a common rail diesel engine, a relief valve, which discharges accumulated fuel on an as needed basis, is located in the delivery pipe to prevent excessive increase of the fuel pressure in the delivery pipe.
According to the delivery pipe in which the relief valve is provided, air easily enters the delivery pipe when the engine is not operating. That is, if flow of fuel in and out of the delivery pipe is stopped when the engine is not operating, the fuel temperature in the delivery pipe temporarily increases due to the residual heat of the internal combustion engine. At this time, in the delivery pipe in which the relief valve is provided, increase of the internal pressure of the delivery pipe due to the thermal expansion of fuel causes the relief valve to be opened and part of fuel in the delivery pipe to be discharged. If the temperature of the residual fuel is decreased in accordance with decrease of the temperature of the internal combustion engine in a state where the amount of the residual fuel in the delivery pipe has been decreased, the internal pressure of the delivery pipe is significantly decreased causing air to enter the delivery pipe from a gap in the relief valve. If an operation for restarting the internal combustion engine is started in this state, that is, when the restarting operation is started with air in the delivery pipe, a time required for increasing the fuel pressure in the delivery pipe for preparation of starting the engine is increased as compared to a case where air is not in the delivery pipe.
In an in-cylinder injection internal combustion engine, since the fuel pressure required for fuel injection is high, the delivery pipe is located in the vicinity of a cylinder block. Therefore, in the in-cylinder injection internal combustion engine, the temperature of residual fuel is easily increased after the internal combustion engine is stopped. Thus, the problem is more serious.